Which is better and why?

I know the 577 well but not the 12b rifle round.

The 12b is 1.5 lbs heavier, does this mean it is a more potent round?

Am i correct in thinking both will average around 3,800 ft lbs muzzle energy?

I have had a quote on restoring the very rough 12b to spotless condition, at 6,000 dollars.

The 577 is also rough, but could come in at less i suppose.

Its a toss up between the two.

12b is 800$ and the 577 is 3000$, the latter will end up bringing them level in cost i reckon.

Many thanks

Ben